1. FIELD OF THE INVENTION
The present invention relates to a method of producing a crystallized glass (glass-ceramics) from a phosphate glass.
2. DESCRIPTION OF THE PRIOR ART
The method of producing a calcium phosphate glass especially a calcium phosphate type crystallized glass has been proposed by the inventors in Japanese Examined Patent Publication No. 11625/1980. The resulting crystallized glass has been expected to be useful for ceramic materials for living bodies such as false teeth and artificial bones for surgery.
In accordance with the proposed method, the crystallized glass having a crystallinity of 20% or more is produced by melting, forming and heat-treating a glass having a formulation of 28 to 57 wt. % of CaO and 72 to 43 wt. % of P.sub.2 O.sub.5 if necessary, with Al.sub.2 O.sub.3, SiO.sub.2 and/or B.sub.2 O.sub.3 at a ratio of 10 wt. % or less to said components. In the crystallized glass obtained by the method, the crystals are grown at random and the crystallized glass has high compressive strength as 3000 to 5000 kg/cm.sup.2, but has low bending strength in an order of about 500 kg/cm.sup.2. Therefore, the fragility as a characteristic of ceramics is not improved.
It has been found that a crystallized glass made of .beta.-Ca(PO.sub.3).sub.2 crystals oriented in an elongated direction is obtained by elongating a rod made of a metaphosphate glass such as Ca(PO.sub.3).sub.2 glass at a temperature higher than a glass transformation point by 30.degree. to 40.degree. C. under a tension and then, heat-treating it at a temperature around the glass transformation point or lower. (Nature Vol. 282 No. 5734 pp. 55-56 Nov. 1, 1979).